Is my RIR a banty?

Is there any way to tell if my 16 week old RIR is a bantam? I am new to chickens, so I only know what I have read and researched. From what I know, at full maturity she is supposed to weigh like 6 pounds. She doesn't even weigh a pound yet, and she is noticeably lighter than my Australorp (which, I read, is supposed to be about the same size as a RIR at full maturity). Excuse the pun, but she truly feels light as a feather.

The feed store we bought our girls from didn't say anything about the chicks being bantam, but I am starting to *naively* suspect it. Maybe I am jumping the gun, I don't know.

Sassy, the BO, is quite a bit bigger than the other girls, but BO's are a slightly bigger breed with fluffy feathers anyway. But you can see that June Bug, my Australorp, is bigger than Wyoma, my RIR. Sorry about the pic, I don't have any of them standing on the ground because I can't seem to get them to hold still long enough when they are running around lol.

We are thinking so too. Less than a pound at 4 months old, we are finding it difficult to believe she will blow up to 5 or 6 pounds when she is fully grown. We will know better next time when we are ready to build on our flock. Not that we don't love our girls with all our hearts, we were just hoping for full size girls to give us full size eggs.